Noise reduction apparatus

ABSTRACT

Noise reduction apparatus comprising, encoder, having a memory for storing picture data of a different picture that was formed from a current picture and a reference picture and a motion detector for detecting the motion between the current picture and the reference picture on block by block basis, for encoding the current picture data or for predictive-encoding the inter-pixel difference between blocks of the current picture data and the reference picture data blocked based on the results of the motion detection, a correlation calculator for calculating at least an additional correlation between a first correlation and a second correlation. The first correlation is between a block-of-interest in the current picture used for the predictive encoding and the reference picture block. The second correlation is between blocks on the periphery of the block-of-interest and the reference picture block, a coefficient calculator for generating a noise coefficient for reducing the noise based on at least the second correlation between the first and second correlations, a noise extractor for extracting the noise component based on the inter-pixel difference between the current picture data and the reference picture data, and the noise coefficient, and subtractor for subtracting the noise component from the input picture data so as to cancel the noise.

FIELD OF THE INVENTION

The present invention relates to the noise reduction apparatus adaptedfor an encoder and a decoder.

BACKGROUND OF THE INVENTION

Conventionally there have been various systems for reducing the noisecontained in the video signal. For instance, one system extracts thenoise components from the input video signal and subtracts the noisecomponents extracted from the current video signal so as to be able toreduce the noise. The noise components can be extracted from for examplenon-correlation component between adjacent horizontal scan lines of thevideo signal, a field non-correlation component or a framenon-correlation component. The noise reduction apparatus of this naturemay be configured in a recursive type or a non-recursive type.

Recently, a digital processing of the picture information has beenresearched in the aspect of requirement of high picture quality. Whenthe picture is digitized, the data amount of the picture becomes huge.Thus, it is necessary to compress the data for recording andtransmitting the data. As the compression method is a high efficiencyencoding system that adapts a transform encoding such as a DCT (discretecosine transform) encoding which has a high compression efficiency and alow main current is currently the compression technique. In the highefficiency encoding system, an input picture signal is divided intoblocks each comprised of 8×8 pixels, so as to implement a DCT processingon the DCT blocks on such block by block basis.

This system adapts not only an intra-frame compression which carries outcompressions within each frame by the DCT processing but also aninter-frame compression for reducing the redundancy in a time-axisdirection using the inter-frame correlation. The inter-frame compressionis used to calculate a frame difference between the two successiveframes and implement DCT processing for the differential value using thenature that the general motion pictures of two successive frames aresimilar. Particularly, a motion compensated inter-frame predictiveencoding for reducing the prediction error by predicting the picturemotion and calculating the inter-frame difference is available.

In such a compression apparatus noises caused by a quantization(quantization noise) are also generated. As a solution, Japanese PatentApplication; Tokkai-Hei 4-88795 proposes an apparatus for reducingnoises by specifying noise reduction characteristics suitable for aluminance signal and a chrominance signal respectively. Japanese PatentApplication; Tokkai-Hei 5-227431 proposes methods for detecting andreducing a mosquito noise which occurs in decoding of the encoded datausing DCT. Japanese Patent Application; Tokkai-Hei 4-88795 proposes adecoder in which noise reduction parameters are compared to each otherfor the chrominance signal and the luminance signal.

Further, Japanese Patent Application; Tokkai-Sho 61-288678 proposes amethod for reducing the quantization noise by a suitable predictionvector information at the predictive encoding. Japanese PatentApplication; Tokkai-Hei 6-224773 proposes a method for generating noisereduction coefficients responding to quantized outputs and the resultsof the picture motion detection.

FIG. 15 is a block diagram showing the conventional noise reductionapparatus which is suitable for the encoder and the decoder of themotion picture. FIG. 16 is a block diagram showing a detailedarrangement of an encoder/decoder 39 shown in FIG. 15. Anencoder/decoder 4 shown in FIG. 16 is a combination of the devices whichare proposed in Japanese Patent Applications; Tokkai-Sho 61-288678 andTokkai-Hei 6-224773.

A picture signal input through an input terminal 1 is applied to amemory 2 so as to be memorized. From the memory 2, a block of picturedata, for example, comprised of 8 pixels along a horizontal scan line×8lines along in the vertical direction read-out and applied to theencoder/decoder 4 via a subtracter 3. The encoder/decoder 4 encodes theinput picture data by the DCT processing, quantization processing andthe variable length encode processing and outputs the encoded datathrough an output terminal 11. Further, the encoder/decoder 4 restoresthe original picture by decoding the encoded data and outputs thedecoded data to the adder 5.

The picture data from the memory 2 is also applied to a motion detector9. As mentioned above, the motion detection is implemented in thepredictive encoding. To the motion detector 9, a picture data of theformer frame is applied for example, from a memory 8. The motiondetector 9 detects the motion of the picture on a block by block basisby controlling the reading-out of memories 2 and 8 in cooperation with amemory controller 10, so as to provide a motion vector to a memorycontroller 11 and the encoder/decoder 4. In the inter-frame compressionmode, the memory controller 11 controls the reading-out of the memories2 and 8 based on the motion vector.

It is assumed that the intra-frame compression mode is designated. Inthis case, a switch 6 selects terminal b and applies "0" to thesubtracter 3. Thus, the picture data of the current frame (currentsignal) is applied to the encoder/decoder 4. The current signal isencoded in the encoder/decoder 4 and then outputted from an outputterminal 7. And, the encoder/decoder 4 decodes the encoded data andapplies it to an adder 5. To the adder 5, "0" is applied from the switch6, and the adder applies the decoded picture data to the memory 8 as itis.

It is assumed that the inter-frame compression mode is designated. Inthis case, the switch 6 selects a terminal a and provides the contentsof the memory 8 to the subtracter 3. The memory 8 wherein the decodedpicture data of the former picture is memorized provides the storedblock picture data at the blocking position based on the motion vectoras the motion compensated reference picture data. The subtracter 3carries out a subtraction between the current signal and the motioncompensated reference data so as to calculate the prediction error. Theencoder/decoder 4 encodes the prediction error from the subtracter 3 soas to output the encoded data via the output terminal 7.

The encoder/decoder 4 decodes the encoded data so as to apply thedecoded data to the adder 5. In this case, the reconstituted data of theprediction error is applied to the adder 5. The adder 5 adds the motioncompensated reference picture data from the memory 8 to the predictionerror from the encoder/decoder 4 so as to restore the original pictureand provides the restored original picture to the memory 8. Thus, thereference picture data to be used in the next encoding operation isstored in the memory 8.

Hereinafter, the encoding of the intra-frame compression mode and theinter-frame compression mode is implemented by the same operationrepeatedly.

The operation of the encoder/decoder 4 will be explained in reference tothe FIG. 16.

The current signal from the subtracter 3 is applied to a DCT unit 15 ofthe encoder/decoder 4. The DCT unit 15 converts the input signal fromthe spatial coordinate axis elements to a frequency component by atwo-dimensional DCT processing for a 8×8 pixel block. Accordingly, it ispossible to reduce the spatial correlation component. That is, theconversion coefficient output from the DCT unit 15 is applied to aquantizer 16, where the conversion coefficient is quantized with apredetermined quantization range. As a result, the redundancy degree ofone block signal is reduced. Here, the quantization range of thequantizer 16 is controlled by a rate controller 21.

The quantized data from the quantizer 16 is applied to a noise reduction(hereinafter referred to NR) unit 17 by a zigzag scan from thehorizontal low and vertical lower area toward a higher area in eachblock. The NR unit 17, as disclosed in the Japanese Patent Application;Tokkai-Hei 6-224773, reduces the noise of the quantized output based onthe inter-frame non-correlation component. The inter-framenon-correlation component is containing the original non-correlationcomponent of the signal and the noise component. For instance, thenon-correlation component is none (zero) in the freeze-frame picture,and the inter-frame non-correlation component is the noise component.The NR unit 17 determines the original non-correlation component of thesignal by the motion vector, and enlarges the NR coefficient as thenoise component is large. The NR unit 17 multiplies the inter-framecorrelation component by the NR coefficient and subtracts the result ofthe multiplication from the quantized output so as to reduce the noise.

The output from the NR unit 17 is applied to a variable length coder(hereinafter referred as VLC) 18. The VLC 18 outputs the encoded data bythe Huffman encode for the quantized output based on the predeterminedvariable length code table such as a Huffman code table for instance.Here, in the Huffman encoding, a combination data of the number of "0"succession in the quantized output last (zero run-length) and the bitnumber of the non-zero coefficient is encoded. Thus, the short bit isassigned to the data which have a high appearance probability, and thelong bit is assigned to the data having the low appearance probability.As a result, the transmission data amount will be reduced further more.

The encoded output from the VLC 18 is applied to a buffer 19. The buffer19 which is constructed by a first-in first-out memory, outputs theinput encoded data to the output terminal 7 with a predetermined rate.The generating rate of the encoded output from the VLC 18 is thevariable rate. The buffer 19 accommodates the difference between thegenerating rate of the encoded data and the transmission rate of thetransmission channel. Here, the output from the VLC 18 is applied to arate controller 21 also. The rate controller 21 controls thequantization range of the quantizer 18 based on the amount of the codesgenerated from the VLC 18 so as to control the generating rate of theencoded data.

The output from the NR unit 17 is also applied to an inverse-quantizer22 to make the reference picture. The quantized output from the NR unit17 is inverse-quantized in the inverse-quantizer 22, and implemented theinverse-DCT processing in an inverse-DCT unit 23, so as to restore theoriginal picture data. Here, as mentioned above, the output from theinverse-DCT unit 23 is also the prediction error in case of that theoutput of the subtracter 13 is the prediction error. The output of theinverse-DCT unit 23 is applied to a non-linear circuit (hereinafterreferred to NL) unit 24.

The NL unit 24 , as disclosed in Japanese Patent Application; Tokkai-Sho61-288678, eliminates the quantization distortion (quantization noise)caused by the quantization processing. The NL unit 24 improves the S/Nby controlling its output when the level of the inter-framenon-correlation component is small, and reduces the over-shoot on theedge portion by controlling its output when the level is large. The NLunit 24 determines the level of the inter-frame non-correlationcomponent by the motion vector, and controls the non-linearcharacteristics based on the motion vector, so as to reduce the noise bycorresponding with various kinds of pictures. For example, it ispossible to reduce the noise clinging on a flat part and that of thefreeze part inside of the block containing the movable edge partappropriately. The output of the NL unit 24 is applied to the adder 5.

As mentioned above, in the encoder/decoder 4 as shown in FIG. 16, thenoise caused mainly by the current signal is reduced in the NR unit 17and the noise caused mainly by the quantization, it means the predictionerror is reduced in the NL unit 24. As a result, the encoded data whichis reduced the noise is obtained.

However, the NR unit 17 and the NL unit 24 determines the levels of theinter-frame correlation components by the motion vectors, and theparameters for deciding its characteristics are controlled on the motionvector on detection by detection basis. That is, the parameter forreducing the noise is changed on block by block basis. As a result,though the noise caused by the predicted distortion and the currentsignal is reduced, there will be differences of the noise reductioneffect on block by block basis. So, there was a drawback that aflickering caused by the differences of the noise reduction effectappears on the picture.

As described above, in the conventional noise reduction apparatusmentioned above had a problem that the noise reduction parameter iscontrolled by the motion detecting on block by block basis, and thenoise reduction effects of every block are different. As a result, theflickering in block appears on the picture.

SUMMARY OF THE INVENTION

It is, therefore, an objective of the present invention to provide anoise reduction apparatus which has enough noise reduction effect andalso prevents occurrences of visible picture flickering in each block.

In order to achieve the above object, a noise reduction apparatusaccording to one aspect of the present invention includes an encoder,having a memory for storing picture data on a different picture from acurrent picture as that of a reference picture and a motion detector fordetecting the motion between the current picture and the referencepicture on a block by block basis, for encoding the current picture dataor for predictive-encoding the inter-pixel difference between blocks ofthe current picture data and the reference picture data blocked based onthe results of the motion detection, a correlation calculator forcalculating at least a second correlation between a first correlationbetween a block subjected for the noise reduction processing(hereinafter the block will be referred to as block-of-interest) in thecurrent picture used for the predictive encoding and the referencepicture block, and the second correlation between blocks on theperiphery of the block-of-interest and the reference picture block, acoefficient calculator for generating a noise coefficient for reducingthe noise based on at least the second correlation between the first andsecond correlations, noise extractor for extracting the noise componentbased on the inter-pixel difference between the current picture data andthe reference picture data, and the noise coefficient, and a subtractorfor subtracting the noise component from the input picture data so as tocancel the noise.

In order to achieve the above objective, a noise reduction apparatusaccording to another aspect of the present invention includes a decoder,to which the encoded data caused by the encoding of only the currentpicture data or by the predictive encoding of the inter-pixel differencebetween blocks of the current picture data and the reference picturedata are inputted, not only for decoding the current picture data andthe inter-pixel difference by decoding the encoded data but also thecurrent picture data by adding the decoded difference between pixels tothe reference picture data read-out from the memory by using the memoryfor storing the reference picture data, a correlation calculator, towhich outputs are applied from the decoder and the memory, forcalculating at least a second correlation from a first correlationbetween the block-of-interest in the current picture and the second onebetween the blocks near the block-of-interest in the current picture andthe reference picture block, a coefficient calculator for generating anoise coefficient based on at least the second correlation between thefirst and the second correlations to reduce the noise, a noise extractorfor extracting the noise components based on the inter-pixel differencebetween the current picture data and the reference picture data and thenoise coefficient, and a subtractor for eliminating the noise bysubtracting the noise component from the picture data to be input.

In the noise reduction apparatus of the first aspect, the correlationcalculator calculates at least a second correlation between blocks onthe periphery of the block-of-interest and the reference picture blockwithin a first correlation between the block-of-interest in the currentpicture and the reference picture block and the second correlationbetween the blocks on the periphery of the block-of-interest and thereference picture block.

The noise extractor extracts the noise component based on the picturedata of the current picture and the that of the reference picture andthe

Since the noise coefficient is generated using the second correlationbetween the reference picture block and the blocks on the periphery ofthe block-of-interest in the current picture, the dispersion of theextracted noise components in each block is low.

The subtractor cancels the noise components in the picture data andapplies it, for example, to the encoder. Thus, the encoded data from theencoder has a small difference of noise eliminating effects in eachblock.

In the noise reduction apparatus of the second aspect, the decoderrestore the original picture data from the encoded data.

The correlation calculator to which the picture data from the decoderand the reference picture data from the memory are inputted, calculatesat least a second correlation between a first correlation between thecurrent picture block and the reference picture block and the secondcorrelation between the block-of-interest in the current picture and thereference picture block.

The coefficient calculator generates the noise coefficient based on atleast the second correlation between the first and the secondcorrelation.

The noise extractor extracts the noise component based on theinter-pixel difference between the current picture data and thereference picture data and the noise coefficient. Since the noisecoefficient is generated using the second correlation between thereference picture block and the blocks on the periphery of theblock-of-interest in the current picture, the dispersion of theextracted noise component in each block is small.

The subtractor cancels the noise component in the picture data so as toapply to the memory. Thus, the decoded picture data from the decoder hasa small difference of noise eliminating effects in each blocks.

Additional objective and advantages of the present invention will beapparent to persons skilled in the art from a study of the followingdescription and the accompanying drawings, which are hereby incorporatedin and constitute a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a block diagram showing one embodiment of the noise reductionapparatus according to the present invention;

FIGS. 2A and 2B are flow charts for explaining the motion detection;

FIG. 3 is a flow chart for explaining the motion detection;

FIG. 4 is a flow chart for explaining the motion detection;

FIG. 5 is a flow chart for explaining the average of the correlations;

FIG. 6 is a graph showing the relationship between the motion vector andthe correlation;

FIG. 7 is a graph for showing the relationship between the motion vectorand the correlation in the conventional system;

FIG. 8 is a graph for explaining the effect of the embodiment shown inFIG. 1;

FIGS. 9A to 9C are is a flow charts for explaining the motion of theembodiment of FIG. 1;

FIG. 10 is a block diagram showing another embodiment of the presentinvention;

FIG. 11 is a block diagram showing another embodiment of the presentinvention;

FIG. 12 is a block diagram showing another embodiment of the presentinvention;

FIG. 13 is a flow chart for explaining the inter-pixel correlation;

FIG. 14 is a block diagram showing another embodiment of the presentinvention;

FIG. 15 is a block diagram showing the conventional noise reductionapparatus; and

FIG. 16 is a block diagram showing the detailed arrangement of theencoder/decoder 4 in FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained in detailhereinafter in reference to the attached drawings. FIG. 1 is a blockdiagram showing one embodiment of the noise reduction apparatusaccording to the present invention. In FIG. 1, the same components asthose shown in FIG. 15 are assigned with the same marks.

A picture signal is inputted input terminal 1. The picture signal isapplied to a memory 2 and memorized on frame units. The memory 2reads-out the picture data on a block by block basis. Each block each,for example, comprises 8×8 pixels in both horizontal and verticaldirections. The picture data from the memory 2 is applied to not only a.noise reduction unit 32 via a terminal I of a switch 31, but also to amotion detector 9 and a subtracter 37. The switch 31 selects theterminal I and provides "0" to a subtracter 33 in the intra-framecompression mode, and selects a terminal P and provides the predictionerror from the subtracter 37(described after) to the subtracter 33 inthe inter-frame compression mode. The subtracter 37 calculates theprediction error and the non-correlation component. The motion detector9 detects the operation of the input picture signal and outputs not onlythe motion vector but also the signal showing the inter-framenon-correlation component.

FIGS. 2 through 4 illustrate the motion detector 9 shown in FIG. 1. FIG.2a shows the current frame picture and the FIG. 2b shows the referenceframe picture.

To the motion detector 9, the current frame picture data from the memory2 and the reference frame (reference picture) picture data from a memory8 (as described later) are input. The motion detector 9 implements themotion detection in block by block base. For instance, if it is assumedthat the DCT block is comprised of 8×8 pixels, and four luminance DCTblocks have the same size with one chrominance difference DCT block by asampling frequency difference between the luminance signal and thechrominance difference signal, the motion detector 9 implements themotion detection on the four luminance DCT blocks (equals to onechrominance difference DCT block), that is, macroblocks comprising 16×16pixels, on block by block basis.

It is assumed that the motion of the block-of-interest (macro-block) 53which encodes a current frame 51 as shown in FIG. 2a is detected. Inthis case, the motion detector 9 takes the relative positionrelationship of the block-of-interest 53. Here, a search area 55centering around the block 54 of a reference frame 52 is set up. FIG. 3shows the expansion of the search area 55 shown in FIG. 2a. In FIG. 3,the search area 55 takes the dimensions of 47×47 pixels.

The motion detector 9 searches the block having most resembling patternto the pattern of the block-of-interest 53 of the current frame 51inside of the search area 55. That is, the motion detector 9 sets up theblocks in turns by moving them on pixel by pixel basis inside the searcharea 55, and implements the matching operation for accumulating theabsolute value of the difference between pixels which are correspond toeach other between the block 53 and the block defined in the search area55, so as to make the block which has the smallest accumulating value asa reference picture block.

FIG. 4 shows the 1 pixel in the block 54 within the search area 55. Thepixel 57 is an arbitrary pixel in the block 54. FIG. 4 shows the areawhere the pixel 57 and other pixel to be carried out the matchingoperation therebetween are able to take in the search area 55. That is,a matching operation is carried out between the pixel 57 and 32×32pixels. So, there are 32×32=1024 blocks which are able to be set upwithin the search area 55.

The motion detector 9 calculates the vector 58 showing the positionrelationship between the block 54 and the reference picture block whichis a block having the smallest accumulated value calculated by thematching operation as the motion vector. The motion detector 9 providesnot only the calculated motion vector to a memory controller 11 and theencoder/decoder 39, but also the correlation between the referencepicture block which are calculated on the process of the motion vectoroperation and the current frame block to a correlation averagecalculator 35 of a noise reduction unit 32.

In the embodiment, it is using the correlation calculated on the processof the motion detection. However, it may use that calculated by otherprocessing. By using the correlation calculated on the motion vectoroperation, it can make the hardware for the correlation calculationuseless, and also it makes the processing time for the correlationcalculation shorter.

A memory controller 10 controls the read-out of the memories 2 and 8 inthe motion detecting time controlled by the detector 9. Further, amemory controller 11, to which the motion vector frame the motiondetector 9 is applied, controls the read-out of the memory 8, so as todesign the blocking position of the reference block. Further, the memorycontroller 11 outputs the controlling signal for controlling the storingand calculating process timing in the correlation average calculator 35.The subtracter 37, to which the current frame picture data from thememory 2 and the reference picture data from the memory 8 are applied,carries out a subtraction between the current and reference picture dataso as to produce the inter-frame correlation component to be applied toa noise extractor 34. The subtracter 37, to which the current block dataand the reference block data are applied from the memories 2 and 8 also,carries out a subtraction between the current and reference picture dataso as to produce the prediction error to be applied to a terminal P of aswitch 31.

The noise reduction unit 32 is comprised of the subtracter 33, the noiseextractor 34, the correlation average calculator 35 and the coefficientcalculator 36. The picture data from the switch 31 is applied to thesubtracter 33 of the noise reduction unit 32. The inter-framenon-correlation component from the subtracter 37 is applied to the noiseextractor 34. In the noise reduction unit 32, the noise extractor 34extracts the noise component based on the inter-frame non-correlationcomponent and the NR coefficient, while the subtracter 33 subtracts thenoise component from the input picture data. Thus the noise reductionunit 32 cancels the noise.

In this embodiment, the NR coefficient is calculated not only by thecorrelation between the reference picture block and the current frameblock which is compressing (hereinafter referred to ablock-of-interest), but also by the correlation between the blocks onthe periphery of the block-of-interest the current frame and thereference picture block which correspond to the blocks. FIG. 5illustrates the correlation average calculator 35.

It is assumed that the block-of-interest 61 and its peripheral blocks 62through 65. Further, it is also assumed that the correlation whichcorresponds to the motion vector between the block-of-interest 61 andthe reference block in the reference frames to designated as CMBO (CMBstands for Current Macro Block). Also, respective correlations whichcorrespond to the motion vectors between blocks 62 through 65 and therespective reference frame blocks are designated as CMB1 through CMB4.The correlation average calculator 35, which has a memory storing thecorrelation CMB0 calculated about the block-of-interest 61 in thecurrent frame and the correlations CMB1 through CMB4 calculated aboutthe blocks 62 through 65, calculates the average of these correlationsand provide the average value to the coefficient calculator 36.

The average calculation implemented in the correlation averagecalculator 35 is not limited to the arithmetic averaging. It may beimplemented by the geometrical average calculation, or filteringoperation such as the weighted average.

The coefficient calculator 36 calculates the NR coefficient based on theaverage value of the input correlation. The coefficient calculator 36makes the NR coefficient small when the average value of the correlationis large, and makes it large when the value is small.

The noise extractor 34 extracts the noise component from thenon-correlation component output from the subtracter 37 using the NRcoefficient so as thus applying the noise component to the subtracter33. For instance, the noise extractor 34 extracts the noise component bymultiplying the non-correlation component with the NR coefficient. Thesubtracter 33 subtracts the noise component from the input picture data,and provides the picture data removed the noise component to theencoder/decoder 39.

The encoder/decoder 39 has almost the same components as the FIG. 16,but it does not have the NR unit 17 and the NL unit 24. Theencoder/decoder 39 implements the quantization of the input picture databy the DCT processing and implements the variable-length encode so as tooutput the encoded data through the output terminal 7. Theencoder/decoder 39 implements the inverse-DCT processing by implementingthe inverse-quantization on the encoded data so as to restore theoriginal picture data which is as the same as that before the DCTprocessing and provide the restored picture data to the adder 5. Whenthe prediction error is inputted to the encoder/decoder 39, the picturedata applied to the adder is also prediction error.

The output from the adder 5 is applied to the adder 5 via the memory 8and the terminal P of the switch 38. The memory 8 stores the output fromthe adder 5 as the reference picture data. The switch 38 selects theterminal I and applies O to the adder 5 in the time of the intra-framecompression mode, and selects the terminal P and applies the referencepicture data read-out from the memory 8 to the adder 5 in the time ofthe inter-frame compression mode. In case of the inter-frame mode, theadder 5 adds the decoded data from the encoder/decoder 39 to thereference picture data so as to restore the original picture data andmemorize it to the memory 8.

The operation of the embodiment comprised as described above will beexplained in reference to the graphs in FIGS. 6 through 8 and the flowchart of FIG. 9. In FIG. 6, the relation between the motion vectorcalculated for various kinds of pictures and the correlation by takingthe motion vector amount of the horizontal or vertical direction on thehorizontal axis, and taking the correlation on the vertical axis. InFIGS. 7 and 8, the relation between the motion vector for thequantization and the correlation is shown. FIG. 7 illustrates therelation in the conventional system, while FIG. 8 illustrates therelation in the embodiment of the present invention. Here, the largerthe correlation, the similitude relation of the picture patterns becomeslower. While the smaller the correlation, the similitude relation of thepicture patterns becomes higher. FIG. 9 illustrates the timing chart ofthe various calculations.

The picture signal input via the input terminal 1 is blocked in thememory 2. After that, it is applied to not only to the terminal I of theswitch 31, but also to the subtracter 37 and the motion detector 9.Here, it is assumed that the intra-frame compression mode is specified.In this case, since the switches 31 and 38 select the terminal I, thepicture data from the memory 2 is supplied to the noise reductionapparatus 32 via the switch 31.

The subtracter 37 produces the inter-frame non-correlation component bycarrying out a subtraction between the current frame picture data andthe picture data from the memory 8, and provides the inter-framenon-correlation component to the noise extractor 34. The motiondetecting block 9 calculates the correlation between the referencepicture block data from the memory 8 and the current frame block dataand provides the correlation to the correlation average calculator 35.The correlation average calculator 35 averages the correlationcalculated for the block-of-interest in the current picture flame andthe blocks on the periphery of the block-of-interest.

It is assumed that the correlation average calculator 35 calculates theaverage of the correlation operated for the five blocks including theblock-of-interest of the current frame and four blocks in either sidesof the block-of-interest. FIG. 9 shows the calculation timing of thiscase. FIG. 9a shows the calculation of the correlation, FIG. 9b showsthe average value calculation, and FIG. 9c shows the compressionoperation. Here, the numbers are showing the block numbers forprocessing. These blocks 1, 2, 3, . . . are arranged from the left sideto the right side of the screen.

In FIG. 9, it is assumed that MV1, MV2, MV3, . . . are showing thecorrelations of the blocks 1, 2, 3, . . . which form a line from leftside to right side of the screen. The encode is orderly implemented fromthe left side block to the right side block. Now, it is also assumedthat the block-of-interest is designated by the reference numeral 3. Thecorrelation average calculator 35 stores also correlations MV1 and MV2at the timing of inputting the correlation MV3 which is correspond tothe block-of-interest 3. The correlation average calculator 35 does notcalculate the average value till the correlations MV4 and MV5 which arecorresponding to the two blocks on the right side of theblock-of-interest are input.

The correlation average calculator 35, which is controlled by the memorycontroller 11, calculates the average value M3 among the correlationsMV1 through MV5 as shown in FIG. 9b and provides the average value M3 tothe coefficient calculator 36 when the correlations MV1 through MV5 areinput thereinto. Thus, the compression operation to theblock-of-interest 3 is implemented at the timing of inputting the block7 as shown in FIG. 9.

Here, since the average calculation of the correlations is completed inrelatively short time, its possible to implement the average calculationin the compression processing time. In the case of selecting the blocksin the vertical sides of the block-of-interest as its on the peripheryof blocks, it just causes a greater processing time delay.

The average value of the correlation calculated in the correlationaverage calculator 35 is applied to the coefficient calculator 36. Thecoefficient amount calculator 36 calculates the NR coefficient based onthe average of these correlations and provides the NR coefficient to thenoise extractor 34. The noise extractor 34 multiplies the inter-framenon-correlation component from the subtracter 37 with the NRcoefficient, so as to extract the noise component. The subtracter 33cancels the noise component in the picture data applied through theswitch 31, so as to provide the data removed the noise component to theencoder/decoder 39.

The encoder/decoder 39 encodes the picture data and outputs the encodeddata through the output terminal 7. Further, the encoder/decoder 39decodes the encoded data and applies the decoded data to the adder 5. Inthis case, the switch 38 is selecting the terminal I. As a result, theadder 5 passes the output of the encoder/decoder 39 therethrough as itis. The output of the adder 5 is stored in the frame memory 8 as thereference picture.

It is assumed that the inter-frame compression mode is specified. Inthis case, the switches 31 and 38 select the terminal P. The motiondetector 9m detects the motion on block by block basis by the matchingoperation between the current picture data from the memories 2 and 8 andthe reference picture data. The motion detector 9 not only provides thecalculated motion vector to the encoder/decoder 39, but also the motiondetector 9 calculates the correlation between the current frame blockand the reference picture block and provides the correlation to thecorrelation average calculator 35. The correlation average calculator 35averages not only the correlations regarding to the block-of-interest,but also other four blocks of each two blocks in either back and fourthsides of the block-of-interest, so as to output the average to thecoefficient calculator 36. The coefficient calculator 36 calculates theNR coefficient based on the average value of the coefficient amounts.Then, also in this case, the noise component is extracted based on theaverage value of the coefficient amounts calculated about theblock-of-interest of the current frame and its peripheral blocks. Thedecreasing motion of the noise component is as the same as theintra-frame compression mode.

The subtracter 37 produces the prediction error by carrying out asubtraction between the current block data and the reference pictureblock data, and provides the prediction error to the terminal P of theswitch 31. In the inter-frame compression mode, the subtracter 33cancels the noise component from the prediction error applied thereto.The encoder/decoder 39 encodes the prediction error. The adder 5restores the original picture by adding the reference picture data fromthe memory 8 to the decoded prediction error, and stores the restoredpicture data in the memory 8 as the reference picture data to be used ata next encoding operation.

In FIG. 6, the graph A shows a picture pattern of comparatively flat andstationary like a blue sky. The graph B shows a picture pattern of rapidchange and motion. The graph C shows a picture pattern of moving picturehaving the periodically high frequency components. Here, for instance,in the picture pattern which the random noises are superposed on the 50%of the white signals, the characteristics will be fixed value inproportion to the noise amount (not shown).

FIG. 7 shows the difference of characteristics between the each blocksand each frames which are adjacent to in the picture pattern of graph Bin FIG. 6., The graphs Al and B1 are showing the picture patterns of thepredetermined two blocks a and b which adjoin with each other in FIG. 7.The graphs A2 and B2 are showing the quantized picture data of theblocks a and b in the conventional embodiment.

As shown in the graphs A1 and B1 in FIG. 7, each blocks a and b nest tohave the comparatively same character in the relation between thecorrelations and the motion vector amounts before the quantization.However, in case of the quantization for the compassing s shown in thegraphs A2 and B2, the character between the adjoining blocks a and b hasa great difference. That is, when the quantization range is relativelynarrow or the quantization is not implemented, the dispersion of thecorrelations and the vector amounts between adjoining blocks will begreat compared that the quantization range is relatively wide. Thisdispersion is supposed to be caused by the quantization distortion.

FIG. 8 shows the characteristics of the embodiment with the motionvector amount shown on the axis of abscissas and the correlationsbetween the reference picture block and the current picture block on theaxis of ordinates. The graphs C1 and C2 in FIG. 8 shows the picturepattern of the blocks a and b which are nest to each other, both ofwhich are showing the picture pattern of rapid change and motion And,the graphs C1 and C2 are showing the character when there are no noiseand quantization error.

At block a, as shown in graph C1, in the relation between the motionvector and the correlation, the more the coordinates goes away from theminimum value dot h, the greater the value becomes. That is, the dot hshows the reference picture block having a minimum correlations to theblock-of-interest a. At the adjacent block b, as shown in graph C2, inthe relation between the motion vector and the correlation, the more thecoordinates go away from the minimum value dot i, the greater the valuebecomes. That is, the dot i shows the reference picture block having theminimum correlations to the block-of-interest b. Here, in the motiondetector 9, the vector and scalar amounts at the dots h and i with theminimum correlations are output as their motion vectors.

The correlation average calculator 35 calculates the average of thecorrelations at the dots h and i. The average value of the correlationvalue has a relationship; the correlation at the dot i≧the average ofthe correlations≧the correlation at the dot h.

When there are noises only, or there are both noises and thequantization errors, the coordinates of the motion vectors to the blocksa and b spread out from the centers of the dots h and i. The circles eand f in FIG. 8 are showing the spreading areas.

Generally, the motion vector 5 calculated from the reference pictureblock to the block a and from the reference picture block to the block bhas the same size. This is that when the average of the correlations iscalculated over the research area in FIG. 3, the three half of thereference picture block which can get, in the adjoining blocks.

The direction of the correlations caused by the noise and thequantization is generated at random. That is, the correlations of theblock a and its reference picture block can be shown by an arbitrary dotin the circle e, and the correlations of the block b and its referencepicture block can be shown by an arbitrary dot on the circle f. Sincethe dispersion becomes random, the dispersion amounts of the averagevalue between each blocks a and b and these each reference pictureblocks are highly possible to be converged in comparatively small value,which might be smaller than the dispersion amounts of each correlationsbetween the blocks a and b and these each reference picture blocks.Thus, the dispersion of the average value of the correlations betweenthe blocks a and b and each these. reference picture blocks can be shownby circles smaller than the circles e and f. That is, by taking anaverage, the low-pass filter characteristics is given, and thedispersion of the average value of the correlations becomes smaller.

Accordingly, its better to use the average of the correlationscalculated for the block-of-interest and its peripheral blocks ratherthan the correlation of only the block-of-interest for reducing theflickering of each block.

When there is no noise, and only the quantization error is generated,the dispersion of the motion vector does not make a circle, and expandin the predetermined direction in a specific picture pattern. However,since the picture patterns themselves are not the same in the randomprocess, it can reduce the flickering in each block by averaging thedispersion amounts to reduce them.

Accordingly, in the embodiment, it calculates not only the correlationsbetween the block-of-interest of the current frame and the referencepicture block, but also the correlations between the blocks on theperiphery of the block-of-interest and their own reference pictureblocks. As a result, it cancels the noise component based on the averagevalue of these correlations. This average of the correlations hassmaller dispersion than that between each block-of-interest and theirreference picture blocks. That is, by controlling the parameter of thenoise reduction using the block-of-interest and its peripheral blocks,it can make the noise reduction effects difference between blockssmaller than the case of controlling the parameter for noise reductionon block by block basis. As a result, it can prevent the flickering ofeach block appearing on the picture.

FIG. 10 is a block diagram showing another embodiment of the presentinvention. This embodiment shows the example which is appropriate to thedecoding apparatus for decoding the encoded data which are encoded byadapting the predictive encoding.

The encoded data from the encoding system containing the inter-frameencoding are applied to a variable length decoder 161. The variablelength decoder 161 implements the variable length decode to the inputencoded data and applies them to an inverse-quantizer 162. Theinverse-quantizer 162 restores the data before the quantization by theinverse-quantization processing and provides the restored data to aninverse-DCT unit 163. The inverse-DCT unit 163 restores the pixel databefore the DCT processing by the inverse-DCT processing of theinverse-quantized output and provides the restored pixel data to anadder 164. Here, the variable length decoder 161 implements the variablelength decode to the motion vector of the input encoded data to beoutput therefrom.

The switch 165 selects the terminal I at the intra-frame compressionmode and provides "0" to the adder 164, and at the inter-framecompression mode, it selects the terminal P and provides the motionguaranteed reference picture block data from memories 81 and 82(mentioned later) to the adder 164. The adder 164 restores the originalpicture data by adding the output from the inverse-DCT unit 163 with theoutput from the switch 165.

The output from the adder 164 is applied to a subtracter 68 via a delaymemory 67 of a noise reduction unit 66. The subtracter 68, to which thenoise component is applied from a noise extractor 74 (mentioned later),cancels the noise component in the decoded picture data, and providesthem to the memories 81 and 82 via the switch 80. The contents of thememories 81 and 82 are output as the decoded picture data via the switch83. The blocking positions of the switches 81 and 82 are controlledbased on the motion vector, and the stored decoded picture data areoutput via the switch 84 as the motion guaranteed reference pictureblock data. The switches 80, 83, and 84 are changed by connected witheach other, when the write-in is implemented in one of the memories 81and 82, the read-out is implemented from the other one. The referencepicture block data from the memories 81 and 82 are applied to theterminal P of the switch 165, the subtracter 69 and the correlationcalculator 70 via the switch 84.

In the embodiment, the noise reduction unit 66 comprised of thesubtracters 68 and 69, the correlation calculator 70, the delay memories67 and 73, the correlation average calculator 71, the coefficientcalculator 72 and the noise extractor 74. To the correlation calculator70 the motion vector transmitted in conjunction with the encoded data isapplied. The correlation calculator 70 calculates the correlationbetween the current frame block data and the reference picture blockdata from the motion vector and provides the correlation to thecorrelation average calculator 71. In this embodiment, the correlationaverage calculator 71 memorizes not only the correlation of theblock-of-interest of the current frame, but also the correlationcalculated about the blocks on the periphery of the block-of-interest,and it calculates the average value of these correlations. Thecorrelation average calculator 71 provides the average of thecorrelations to the coefficient calculator 72. The coefficientcalculator 72 generates the NR coefficient based on the average of somecorrelations and provides the NR coefficient to the noise extractor 74.

The current frame block data and the reference picture block data arealso applied to the subtracter 69. The subtracter 69 produces thedifference between these two block data as the inter-framenon-correlation component, and then provides the inter-framenon-correlation component to the noise extractor 74 via the delay memory73. The delay memories 67 and 73 delay input data by about thecalculation time of the correlation average calculator 71. The noiseextractor 74, for instance, extracts the noise component by multiplyingthe inter-frame non-correlation component with the NR coefficient andprovides the noise component to the subtracter 68.

The operation of the embodiment in such arrangement as mentioned abovewill now be explained.

The encoded data are subjected to the variable length decode in thevariable length decoder 161. The output from the variable length decoder161 is implemented inverse-quantization in the inverse-quantizer 162,then implemented the inverse-DCT processing in the inverse-DCT unit 163so as to restore the original pixel data. When the encoded data havebeen implemented the predictive encoding the output from the inverse-DCTunit 163 is prediction error. In this case, the adder 164 adds thereference picture block data from the memories 81 and 82, and the outputfrom the inverse-DCT unit 163 so as to restore the original picture. Thedecoded picture data from the adder 164 are applied to both thesubtracter 69 in the noise reduction unit 66 and the correlationcalculator 70.

Both the subtracter 69 in the noise reduction unit 66 and thecorrelation calculator 70 are also applied the outputs from the memories81 and 82. The subtracter 69 produces the inter-frame non-correlationcomponent by carrying out a subtraction between the reference pictureblock data from the memories 81 and 82 and the current frame block data,and then provides the inter-frame non-correlation component to the noiseextractor 74 via the delay memory 73. The correlation calculator 70calculates the correlation between the reference picture block and thecurrent frame block and provides the correlation to the correlationaverage calculator 71. The correlation average calculator 71 memorizesnot only the block-of-interest, but also the correlations of the blockson the periphery of the block-of-interest, and it calculates the averagevalue of these correlations. The average value is applied to thecoefficient calculator 72.

In the coefficient calculator 72, the noise coefficient based on theaverage value of the correlations is calculated and applied to the noiseextractor 74. In the noise extractor 74, the noise component isextracted by multiplying the non-correlation component by the NRcoefficient. The subtracter 68 subtracts the noise component from theinput decoded picture data and provides the difference via the delaymemory 67.

The output from the noise reduction unit 66 is memorized in the memories81 and 82 via the switch 80. The picture data stored in the memories 81and 82 are output as the decoded picture data via the switch 83.

If the input encoded data is resulted from the intra-frame compression,the switch 165 applies "0" to the adder 164. The adder 164 applies theoutput of the inverse-DCT unit 163 to the noise reduction unit 66 as itis. Other operations are the same as that in the case that theinter-frame compression encoded data are input.

As described above, in this embodiment, the correlation averagecalculator 71 averages the correlation of the block-of-interest ofcurrent frame block and its reference picture block and those of theblocks on the periphery of the block-of-interest and their own referencepicture blocks. The coefficient calculator 72 calculates the NRcoefficient based on the average of these blocks. Accordingly, it can beable to reduce the flickering of each block.

Here, in this embodiment, the correlation calculator 70 calculates thecorrelation between the reference picture block and the current frameblock. However, by calculating these amount at the encoding time andtransmitting them, it becomes possible to omit the calculation of thecorrelation at the decoder section. In this case, the correlationcalculator 70 is not necessary.

Further, in the present embodiment, the noise reducing operations arerecursively implemented by allocating the noise reduction apparatus inthe decoding loop. However, it is obvious that the noise reductionapparatus may also be allocated outside the decoding loop.

FIG. 11 is a block diagram showing a noise reduction unit 91 in anothertype according to the present invention. In FIG. 11 the same componentsas those shown in FIG. 1 are assigned with the same marks.

In the embodiment, the part that the noise reduction unit 91 issubstituted for the noise reduction unit 32 is different from theembodiment in FIG. 1. In the noise reduction unit 91, the parts that thecoefficient calculators 92 and 93 are substituted for the coefficientcalculator 36 as shown in FIG. 1, and a mixer 94 is also provided, indifferent from the noise reduction unit 32 in FIG. 1. The motiondetector 9 produces the correlation between the reference picture blockand the current frame block to the correlation average calculator 35.The correlation average calculator 35 produces the correlation of theblock-of-interest of the current frame to the coefficient calculator 92.Further, it calculates the average of the correlations of the blocks onthe periphery of the block-of-interest and applies it to the coefficientcalculator 92. Here, the correlation average calculator 35 produces thecorrelation and the average value at the same timing.

The coefficient calculator 92 calculates the NR coefficient based on thecorrelation between the block-of-interest of the current picture frameand its reference block and provides it to the mixer 94. The coefficientcalculator 93 calculates the NR coefficient based on the correlationsbetween the blocks on the periphery of the block-of-interest and theirown reference picture blocks and provides them to the mixer 94. Themixer 94 selects one of the NR coefficients output from the coefficientcalculators 92 and 93 or mixes them at a fixed rate, so as to providethe selected NR coefficient to the noise extractor 34.

The operation of the embodiment in such arrangement will now beexplained.

The motion detector 9 applies the correlation between the referencepicture block and the current frame block to the correlation averagecalculator 35. The correlation average calculator 35 memorizes the inputcorrelation and provides the average of the correlation to the blocks onthe periphery of the block-of-interest in the current frame to thecoefficient calculator 93. Also, the correlation average calculator 35provides the correlation to the block-of-interest in the current frameto the coefficient calculator 92. The coefficient calculator 92 producesthe NR coefficient based on the correlation to the block-of-interest,and the correlation calculator 93 produces the NR coefficient based onthe average value of the correlation to the blocks on the periphery ofthe block-of-interest.

The mixer 94, for instance, selects one of the NR coefficients outputfrom the coefficient calculators 92 and 93 and applies it to the noiseextractor 34. When it selects the output of the coefficient calculator93, it is possible to reduce the flickering of each block. However,contrary, it selects the output of the coefficient calculator 92 it ispossible to obtain a proper noise reduction effect for each block.

Further, the mixer 94 mixes the outputs from the coefficient calculators92 and 93 at the proper ratio and applies it to the noise extractor 34,so as to obtain the desirable noise reduction characteristics.

As described above, in this embodiment, it can obtain the same effect asthat shown in FIG. 1, and also it can obtain the noise reduction effectwhich is desired by viewer.

FIG. 12 is a block diagram showing another embodiment of this invention.In FIG. 12, the same components as those shown in FIG. 11 are assignedwith the same marks, and the explanation of them will be omitted.

In this embodiment, a part that the noise reduction unit 98 adopting acoefficient calculator 97 substituting for the coefficient calculator 92is defined is different from the embodiment shown in FIG. 11. Thesubtracter 37 (see FIG. 1) produces the inter-frame non-correlationcomponent by comparing the reference picture data and the current framepicture data from the memories 2 and 8 on pixel by pixel basis. Thesubtracter 37 provides the non-correlation component not only to thenoise extractor 34 but also to the coefficient calculator 97.

The coefficient calculator 97 calculates the NR coefficient based on theaverage value of the single pixel non-correlation component or theplural pixels non-correlation component, so as to provide the NRcoefficient to the mixer 94. The mixer 94 provides one of the NRcoefficients from the coefficient calculators 93 and 97 or the NRcoefficient which is mixed at the predetermined ratio to the noiseextractor 34.

The operation of the embodiment in such arrangement will now beexplained.

The motion detector 9 provides the correlation of the block-of-interestof the current frame and its reference picture block to the correlationaverage calculator 35. The correlation average calculator 35 storestherein the correlation of the block-of-interest, and calculates theaverage of the correlations of the blocks on the periphery of theblock-of-interest, so as to provide the average value to the coefficientcalculator 93. The coefficient calculator 93 calculates the NRcoefficient based on the average value of the input plural correlationsto be output therefrom.

The subtracter 37 detects the non-correlation components between thereference picture data and the current frame picture data on each pixel,and provides the non-correlation components to the coefficientcalculator 97. FIG. 13 illustrates the correlation of each pixel. Theaverage of a difference amount or some difference amounts between thepredetermined pixel (slanting lines area) of the block-of-interest 99 inthe current frame and the pixel (slanting lines area) of thecorresponding block 100 in the reference frame is applied to thecoefficient calculator 97 as the correlation.

The coefficient calculator 97 calculates the NR coefficient based on theaverage value of the signal pixel non-correlation component or theplural pixels non-correlation component. The mixer 94 provides, forinstance, one of the NR coefficient from the coefficient calculators 93and 97 to the noise extractor 34.

Other operations are the same as those shown in FIG. 11.

Further, this embodiment is also used for the noise elimination of thechrominance signal. For instance, it is assumed that the chrominancesignal and the luminance signal are input via the input terminal 1 bybeing time-multiplexed with each other, and each unit is possible tocarry out the time-multiplexing for the luminance signal and thechrominance signal. In this case, the motion detector 9, as the same asthe explanation mentioned above, applies the correlation between theluminance signal of the reference picture block and that of theblock-of-interest in the current frame to the correlation averagecalculator 35. The subtracter 37 produces the non-correlation componentsbetween the current frame chrominance signal and the reference picturechrominance signal on each pixel, and provides the non-correlationcomponents to the coefficient calculator 97 when the chrominance signalis input. The coefficient calculator 97 calculates the NR coefficientbased on the average value of the chrominance signal non-correlationcomponent. Here, the subtracter 37 provides the non-correlationcomponent about the chrominance to the coefficient calculator 97 whenthe chrominance signal is input.

The mixer 94 applies the NR coefficient based on the outputs from thecoefficient calculators 92, 93, and 97 to the noise extractor 34 at thetime of the noise eliminating to the chrominance signal. Thus, the noiseextractor 34 time-diffusion extracts the noise component contained inthe luminance signal and that contained in the chrominance signal usingthe NR coefficients which are corresponding each luminance signal inputtime and the chrominance signal input time. The subtracter 33 cancelsthe noise component contained in the luminance signal from the inputluminance signal at the time of the luminance signal processing, andalso cancels the noise component contained in the chrominance signalfrom the input chrominance signal at the time of the chrominance signalprocessing, and provides the noise reduced signals therefrom.

Accordingly, in this embodiment, the same effect as that shown in FIGUREis obtained, and further, it can also obtain the desired noise reductioneffect according to the mixing ratio of the mixer 94. Further, it ancontrol the elimination of the noise component on the pixel-by-pixel. Asa result, it is able to implement precise control than the embodimentshown in FIG. 11. It cancels not only the noise of the luminance signalbut also the noise of the chrominance signal. And, it can omit thechrominance motion vector detection device in the noise elimination ofthe chrominance signal.

FIG. 14 is a block diagram showing another embodiment of the presentinvention. In FIG. 14, the same components as those shown in FIGS. 11and 12 are assigned with the same marks, and the explanations of themwill be omitted.

The embodiment of FIG. 14 is different from those as shown in FIGS. 11and 12 in that it comprises a noise reduction unit 101 having thecoefficient calculators 92, 93, and 97 and the mixer 94 in place of thecoefficient calculator 36 shown in FIG. 1.

The mixer 94 provides one of the NR coefficients output from thecoefficient calculators 92, 93, and 97 or the NR coefficient which areobtained by mixing two of them at the predetermined ratio to the noiseextractor 34.

In the embodiment in such arrangement, to the mixer 94, the NRcoefficient based on the correlation between the reference picture blockand the block-of-interest of the current frame, the NR coefficient basedon the correlations between the reference picture block and the blockson the periphery of the block-of-interest of the current frame, and theNR coefficient based on the non-correlation component on pixel-by-pixelbetween the reference picture data and the current frame picture dataare applied . The mixer 94 provides, for instance, a NR coefficientwhich is obtained by mixing these NR coefficients mentioned above at thepredetermined ratio to the noise extractor 34. It is able to obtain thedesirable noise reduction characteristics by defining the mixing ratioof the mixer 94.

In this embodiment also, the luminance signal and the chrominance signalare input via the input terminal 1 by being time-multiplexed with eachother. Thus the subtracter 37 produces the non-correlation components ofeach pixel between the current frame chrominance signal and thereference picture chrominance signal and provides the non-correlationcomponents to the coefficient calculator 97. As a result, it is able tocalculate the NR coefficient of the chrominance signal. Accordingly, inthis embodiment, it can also reduce the noise of the chrominance signal.

As described above, in this embodiment, the same effects as those shownin FIGS. 11 and 12 are also obtained.

In each embodiment, the noise reduction unit is taking the recursivearrangement. However, it is obvious that it can take either recursive ornon-recursive arrangement.

As described above, not only the present invention can provide anextremely preferable noise reduction apparatus which has the enoughnoise reduction effect, but also the present invention has the effect toprevent the visible flickering in each block.

While there have been illustrated and described what are at presentconsidered to be preferred embodiments of the present invention, it willbe understood by those skilled in the art that various changes andmodifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of the presentinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teaching of the presentinvention without departing from the central scope thereof. Therefor, itis intended that the present invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention includes allembodiments falling within the scope of the appended claims.

The foregoing description and the drawings are regarded by the applicantas including a variety of individually inventive concepts, some of whichmay lie partially or wholly outside the scope of some or all of thefollowing claims. The fact that the applicant has chosen at the time offiling of the present application to restrict the claimed scope ofprotection in accordance with the following claims is not to be taken asa disclaimer or alternative inventive concepts that are included in thecontents of the application and could be defined by claims differing inscope from the following claims, which different claims may be adoptedsubsequently during prosecution, for example, for the purposes of adivisional application.

What is claimed is:
 1. A noise reduction apparatus, comprising:encodingmeans, having a memory means for storing picture data of a differentpicture calculated from a current picture and a reference picture, and amotion detecting means for detecting motion between the current pictureand the reference picture on a block by block basis, for encoding acurrent picture data or for predictive-encoding an inter-pixeldifference between blocks of the current picture data and a referencepicture data block based on results of the motion detection; correlationcalculating means for calculating at least an additional correlationbetween a first correlation and a second correlation, wherein the firstcorrelation is between a block-of-interest in the current picture usedfor the predictive encoding and the reference picture block and thesecond correlation is between blocks on a periphery of theblock-of-interest and the reference picture block; coefficientcalculating means for generating a noise coefficient for reducing noisebased on at least the additional correlation between the first andsecond correlations; noise extracting means for extracting a noisecomponent based on the inter-pixel difference between the currentpicture data and the reference picture data, and the noise coefficient;and subtraction means for subtracting the noise component from an inputpicture data so as to cancel the noise.
 2. A noise reduction apparatusas claimed in claim 1, whereinsaid motion detecting means detects thereference picture block by a matching operation of the pixel by pixelamong the blocks within a predetermined search area which are centeringaround the reference picture block on position corresponding to that ofthe block-of-interest in the current picture; and said correlationcalculating means outputs the matching calculating results from themotion detecting means as the first and the second correlations.
 3. Anoise reduction apparatus as claimed in claim 1, wherein the correlationcalculating means and the noise extracting means have memories forstoring the reference picture data, while reading-out the referencepicture data in intra-frame encoding mode.
 4. A noise reductionapparatus as claimed in claim 1 wherein the correlation calculatingmeans and the noise extracting means read out the reference picture datafrom the memory means in the encoding means even in intra-frame encodingmode.
 5. A noise reduction apparatus as claimed in claim 1 wherein thenoise extracting means extracts a noise component based on theinter-pixel difference obtained by the encoding means and the noisecoefficient.
 6. A noise reduction apparatus as claimed in claim 5,whereinan inter-pixel correlation calculating means for generating athird correlation based on an inter-pixel difference between theblock-of-interest in the current picture and the reference pictureblock; said coefficient calculating means for generating a second and athird noise coefficient based on the second correlation calculated bythe correlation calculating means and third correlation respectively;and said noise extracting means uses one of the second or the thirdnoise coefficients as the noise coefficient or uses both of them bymixing at a predetermined ratio.
 7. A noise reduction apparatus asclaimed in claim 6, whereinthe coefficient calculating means generatesnot only the noise coefficient based on one of the first and secondcorrelations calculated for a luminance signal, but also the noisecoefficient to a chrominance signal by a third correlation based on aninter-pixel difference about the chrominance signal obtained by theencoding means, and the noise extracting means extracts the noisecomponent contained in the chrominance signal using the noisecoefficient calculated by using the luminance signal and the noisecoefficient to the chrominance signal.
 8. A noise reduction apparatus asclaimed in claim 5, whereinthe coefficient calculating means generatesnot only first and second noise coefficients based on the first andsecond correlations calculated by the correlation calculating means butalso a third noise coefficient based on a third correlation calculatedby an inter-pixel correlation calculating means, and the noiseextracting means uses one of a first through third noise coefficients asthe noise coefficient or uses at least two of them by mixing at apredetermined ratio.
 9. A noise reduction apparatus as claimed in claim8, whereinthe coefficient calculating means generates not only the noisecoefficient based on one of the first and second correlations calculatedfor a luminance signal, but also the noise coefficient to a chrominancesignal by a third correlation based on an inter-pixel difference aboutthe chrominance signal obtained by the encoding means, and the noiseextracting means extracts the noise component contained in thechrominance signal using the noise coefficient calculated by using theluminance signal and the noise coefficient to the chrominance signal.10. A noise reduction apparatus as claimed in claim 1, whereinsaidcoefficient calculating means generates not only a first noisecoefficient based on the first correlation calculated by the correlationcalculating means but also a second noise coefficient based on thesecond correlation from the correlation calculating means; and saidnoise extraction means uses one of the first and the second noisecoefficients as the noise coefficient or using both of them by mixing ata predetermined ratio.
 11. A noise reduction apparatus as claimed inclaim 1, whereinan inter-pixel correlation calculating means generates athird correlation based on an inter-pixel difference between theblock-of-interest in the current picture and the reference pictureblock; said coefficient calculating means generates not only a secondnoise coefficient based on the second correlation calculated by thecorrelation calculating means but also a third noise coefficient basedon the third correlation; and said noise extracting means uses one ofthe second and the third noise coefficients as the noise coefficient oruses both of them by mixing at a predetermined ratio.
 12. A noisereduction apparatus as claimed in claim 11, whereinthe coefficientcalculating means generates not only the noise coefficient based on oneof the first and second correlations calculated for a luminance signal,but also the noise coefficient to a chrominance signal by a thirdcorrelation based on an inter-pixel difference about the chrominancesignal obtained by the encoding means, and the noise extracting meansextracts the noise component contained in the chrominance signal usingthe noise coefficient calculated by using the luminance signal and thenoise coefficient to the chrominance signal.
 13. A noise reductionapparatus as claimed in claim 1, whereinthe coefficient calculatingmeans generates not only first and second noise coefficients based onthe first and the second correlation calculated by the correlationcalculating means but also a third noise coefficient based on a thirdcorrelation calculated by an inter-pixel correlation calculating means,and the noise extracting means uses one of a first through third noisecoefficients as the noise coefficient or uses at least two of them bymixing at a predetermined ratio.
 14. A noise reduction apparatus asclaimed in claim 13, whereinthe coefficient calculating means generatesnot only the noise coefficient based on one of the first and secondcorrelations calculated for a luminance signal, but also the noisecoefficient to a chrominance signal by a third correlation based on aninter-pixel difference about the chrominance signal obtained by theencoding means, and the noise extracting means extracts the noisecomponent contained in the chrominance signal using the noisecoefficient calculated by using the luminance signal and the noisecoefficient to the chrominance signal.
 15. A noise reduction apparatus,comprising:decoding means, to which encoded data resulting from encodingonly current picture data or by predictive encoding an inter-pixeldifference between blocks of the current picture data and a referencepicture data are inputted, for decoding not only the current picturedata and the inter-pixel difference, but also the current picture databy adding a decoded difference between the inter-pixel difference to thereference picture data read-out from a memory means by using the memorymeans storing the reference picture data; correlation calculating means,to which outputs are applied from the decoding means and the memorymeans, for calculating a first correlation between a block-of-interestin the current picture and a reference picture block and a secondcorrelation between blocks on the periphery of the block-of-interest inthe current picture and the reference picture block; coefficientcalculating means for generating a noise coefficient based on at leastan additional correlation between the first and the second correlationsto reduce the noise, noise extracting means for extracting noisecomponents based on an inter-pixel difference between a current picturedata and a reference picture data and the noise coefficient; andsubtraction means for eliminating the noise by subtracting a noisecomponent from a picture data to be input.